The present invention relates to an electronic timepiece having in the timepiece a secondary battery to be charged from outside the timepiece, and which has an electrostatic protection function for a charge terminal.
In recent years, electronic timepieces have been produced that have generator means such as solar generation means or thermoelectric generation means not requiring battery exchange. These timepieces have structurally provided therein a secondary battery so that generated power is stored in the secondary battery so that the timepiece need to be stopped even when power generation cannot be made. Here, if the secondary battery is small in capacity, there often occur cases in which storage electric power is used up. In order to prevent this, there is a tendency of using secondary batteries, large in capacity. However, where storage electric cower is used up it is difficult to charge the secondary battery up to a level necessary to operate the timepiece. There may be a case where the timepiece is rendered inoperable as the case may be. Due to this, a structure is used to directly charge the secondary battery from the outside thereby preventing such a disadvantage. Also, a timepiece has been put into products structured to charge the secondary battery inside the timepiece directly from the outside without having generator means.
In such a timepiece, because a charging electrode is extended to the outside, there is a possibility of applying an electric shock due to static electricity. A static electricity protection circuit is used to prevent a disadvantage due to electric shock.
The detailed circuit of a conventional static electricity protection circuit is explained using FIG. 1. Also, FIG. 2 shows a block diagram of an electronic timepiece having the conventional static electricity protection circuit. An input terminal 301 is connected to a first external electrode 101 through first connection means 114 of FIG. 2. The input terminal 301 is connected to a resistance 302. The resistance 302 has the other end connected to an output terminal 305, an anode of a third diode 303 and a cathode of a fourth diode 304. The third diode 303 has a cathode that is connected to a positive potential 112 on a positive side of storage means 109. The fourth diode 304 has an anode connected to a reference potential 111 of a negative side of the storage means 109. This reference potential 111 is extended outside the timepiece through the second external electrode 107. The output terminal 305 is connected to an input part of a charge protection circuit 108 through the first diode 103 for reverse flow prevention. On the other hand, the voltage generated by a heat generator 104 is supplied to a booster circuit 105 through second connection means 113. The electric power increased in voltage by the booster circuit 105 is supplied to the input part of the charge protection circuit 108 through the second diode 106. The charge protection circuit 108 has an output connected with the storage means 109 to control the charge to the storage means 109, preventing overcharge of the like. The electric power stored on the storage means 109 is supplied to a timepiece circuit 110, and the timepiece circuit counts and displays a time.
If static electricity enters the input terminal 301, it is reduced in voltage by the resistance 302 and further flows to the third diode 303 or fourth diode 304 thereby reducing over-voltage in a spike form. The effect of static electricity likely to occur at the output circuit 305 or the subsequent is reduced thus preventing breakdown or malfunction.
As charge electrodes an upper case and lower case of an exterior case are used. In this case, because insulation is provided between the upper case and the lower case, there is a case that the static electricity externally entered through the case flows to an electronic circuit inside the electronic timepiece without being immediately discharged to a human body. In order to reduce the effect of the static electricity on the timepiece circuit, the above static electricity protection circuit is used.
However, in the conventional static electricity protection circuit the effect is not sufficient in reducing the effort of static electricity. Although electrostatic breakdown can be prevented, circuit malfunction could not be prevented up to 6 KV of contact discharge in static electricity rating IEC1000-4-2 and 8 KV of in-air discharge.
In routine use, discharge occurs up to approximately 8 KV of contact discharge and 15 KV of in-air discharge as the operation may be. Accordingly, in this case, the conventional static electricity protection circuit could not have prevented malfunction of the timepiece circuit.
It is an object of the present invention to prevent malfunction, breakage or deterioration of an electronic timepiece due to high voltage of about 8 KV of contact discharge or 15 KV of in-air discharge in order not to cause trouble in routine use.
The electronic timepiece of the present invention is characterized in that, in an electronic timepiece having an exterior case structured by storage means, a conductor case and an insulation case, the conductor case is in a structure divided by the insulator case into a plurality wherein each conductor case is electrically in an insulation state. Furthermore, the conductor case is partly, structurally used as an electrode to charge to the storage means thereby enabling external energy of the electronic timepiece to the storage means. In these structures, in order to increase electrostatic withstand voltage, a pattern for discharging static electricity is further provided on a wiring board in a heat generator besides the usual static electricity protection circuit. Also, an air discharge layer is further provided between charge electrodes. This can prevent malfunction, breakage and deterioration of the timepiece circuit.